@Duane: I found an image of a very early typewriter. It has a dial for selecting letters instead of the plate-type mechanism in your photo. It had a serrated bar, as does yours.

Some of the early typewriters were ... interesting to say the least. As I wrote in one of my books (so it must be true):

Some of these weird and wonderful contraptions were as difficult to use as a Church organ, while others printed by keeping the paper stationary and hurling the rest of the machine against it – the mind boggles.

I would have guessed some sort of code generator, but an index typewriter must be close. And for me, Danish would be a secret code. But part of it was missing in the initial picture, which did not help at all. But6 it was fairly obvious in the closeup view that it had something to do with character printing, rather encrypted or not.

Probably the most interesting part is that such a function was fabricated using blacksmith tools.

From this and previous comments and finding the patent number under the US Patents:

the pinch rollers near the bottom of the picture are for holding a wide strip of leather in place.

the lever on the left of the pinch rollers is to permit the leather to be pushed through the pinch rollers a specific distance (like the height of a line of text).

the indexed bar near the top of the photo is to allow the user of the tool to correctly space the lettering from left to right on the leather.

just below this indexed bar is what looks like a jagged saw blade, like you might see on your box of cellophane wrap in your kitchen. It's likely to cut the leather piece off after advancing it far enough to have all the desired lettering in place.

the the leather piece is later mounted on the wheel to indicate who built the wheel, when, and maybe whose wagon it is for. Maybe even information about how the wheel is constructed so someone else can repair it.